DPS Metro Central Question

[KR7CQ]

In the past I have always heard Metro Central at the same signal level with each transmission (unless individual units were using the repeater output for "car to car"). All transmissions were from the Shaw Butte site as far as I knew.

After being out of scanning for a while, I recently started listening again and it seems that this frequency (460.325) is now coming from two or more sites. One is still Shaw Butte I believe, but another one is more distant from my location, quite a bit farther out.

Does anyone know if there are now multiple sites for this frequency and if so where the other site (other than Shaw Butte) is located?

 

[Phoenix805]

460.325 is also used by DPS in district 3 in Holbrook and district 9 in Sierra Vista, but I doubt you're picking them up. I wouldn't think they're using 2 different repeaters in the Phoenix area, but you never know. I'll do a little digging and see if I can find any better info, but I'm not gonna hold my breath.

 

[Phoenix805]

460.325 is also used by DPS in district 3 in Holbrook and district 9 in Sierra Vista, but I doubt you're picking them up. I wouldn't think they're using 2 different repeaters in the Phoenix area, but you never know. I'll do a little digging and see if I can find any better info, but I'm not gonna hold my breath.

 

[Phoenix805]

OK, I'm confused as usual. Hopefully one of the smarter people on here can offer a better explanation. It looks to me like DPS has about 50 base stations and/or repeaters around the state using 460.325. It seems to me like they would have 3 - one for Phoenix, one for Holbrook, and one for Sierra Vista, and maybe 3 backups in case of failures, but 50??

Anyway, looks like they have transmitters on South Mountain and Squaw Peak in Phoenix, White Tanks in the west valley, Thompson Pk in North Scottsdale, and Towers Mountain in Crown King north of the valley. You can probably receive any of these. I wouldn't think they would be intentionally transmitting from two close sites at the same time. Maybe one of them is active when it's not supposed to be?

<waiting for better reply>

Some time when I have some time I'll have to drive around and see what kind of signals I can get in different areas.

 

[KB7MIB]

Wirelessly posted (Opera/9.80 (BREW; Opera Mini/6.0.3/27.2338; U; en) Presto/2.8.119 320X240 LG VN530)

1) Redundacy in case of failure;
2) Coverage of different sections, or beats of a district, especially the larger, more rural districts, like 1, 2 and 3.
It's not unusual for me to hear an officer key up 2 or more sites on Metro West, making the officer's transmission unintelligible. It's like two or more people trying to transmit at the same time, and neither is strong enough to overpower the other, and allow the FM capture effect to work.
The dispatchers only hear one site, because the signals from multiple repeaters are fed to them via wireline, fiber optic, or microwave link, and they go through a voting system, which selects the best audio from one site to be passed through to the dispatcher. The dispatchers can also then select that one site to transmit back to the officer, or they can select multiple, or all sites, so that all other officers out of range of that one site can hear the dispatchers transmission.
Scanner listeners don't have that luxury, and have to deal with multiple signals. I think the officers in the field also have to deal with that issue, if they happen to be within range of two or more sites, when another officer transmits, and may have to have the dispatcher repeat the transmission.

 

[SCPD]

Wirelessly posted (Opera/9.80 (BREW; Opera Mini/6.0.3/27.2338; U; en) Presto/2.8.119 320X240 LG VN530)

1) Redundacy in case of failure;
2) Coverage of different sections, or beats of a district, especially the larger, more rural districts, like 1, 2 and 3.
It's not unusual for me to hear an officer key up 2 or more sites on Metro West, making the officer's transmission unintelligible. It's like two or more people trying to transmit at the same time, and neither is strong enough to overpower the other, and allow the FM capture effect to work.
The dispatchers only hear one site, because the signals from multiple repeaters are fed to them via wireline, fiber optic, or microwave link, and they go through a voting system, which selects the best audio from one site to be passed through to the dispatcher. The dispatchers can also then select that one site to transmit back to the officer, or they can select multiple, or all sites, so that all other officers out of range of that one site can hear the dispatchers transmission.

Scanner listeners don't have that luxury, and have to deal with multiple signals. I think the officers in the field also have to deal with that issue, if they happen to be within range of two or more sites, when another officer transmits, and may have to have the dispatcher repeat the transmission.

I don't understand this because most multiple repeater systems I've either used or have listened to that employs voters only transmits on the repeater that had the best reception. It does little good to transmit on multiple repeaters in order to have all mobile units, no matter what location, be able to hear both sides of the conversation, when doing such sets up what we in the Forest Service called "repeater wars" that results in unintelligible signals. Simulcast systems are another matter and eliminate these wars for the field units. It would seem as though, even if a field unit does not have an optimal signal on the one the voter selects, it would still be able to receive it well enough to copy it.

How many repeaters does Metro Central use? I would think South Mountain covers most of it unless White Tanks does that. It looks like Thompson might be needed up in the northeast portion of the district, however I don't recall if there is one there or on Shaw Butte. Handheld coverage might present some challenges, however, which is one reason using extenders is helpful. But then again, this district would appear to be the easiest in the state to cover.

 

[KB7MIB]

Wirelessly posted (Opera/9.80 (BREW; Opera Mini/6.0.3/27.2338; U; en) Presto/2.8.119 320X240 LG VN530)

From what I understand with voting systems, there is (at least sometimes) an option to allow the dispatcher to manually select one or more transmitter sites, over-riding the system's automatic selection of which transmitter the dispatcher replys to an officer in the field with. How many agencies have that option available, or what any particular agency's policy is for it's actual use, I don't know.
I don't listen to Metro Central that often. I usually listen to Metro West. And once in awhile I will hear what sounds like an officer hitting two or more repeaters. The dispatcher seems to be only replying with one, but they *may* have the ability to select multiple, or all, sites.

 

[KR7CQ]

After reading all of this I am developing my own ideas now.

I know for a fact that Shaw Butte was for a long time the primary (by far) site used, and it covers most of central without any issue. What I have noticed is that over the last year or two they have been using other sites more and more (or so it seems).

The voting system makes a lot of sense as far as explaining what I am hearing also. I sometimes hear a transmission that is full scale, and then the next one (with the same folks talking) is half that strength, and then the very next transmission (from the same dispatcher / unit) is back to full strength, obviously coming from the first site again. As I am imagining it, it's possible that the traffic is switching back and forth between sites at times due to terrain / buildings, as the officer's car is moving through the valley. I also have no doubt that the dispatchers can manually switch sites as needed, complicating things further.

I could have sworn that most if not all of the central traffic USED to come off of just Shaw Butte, as all I ever needed was a portable scanner (I'm close to that site), and I heard everything, every time, and there were no fluctuations in signal strength.

Perhaps the fact that they are now making greater use out of more sites, has to do with the work they are doing on the 700/800 MHz YRCS sites at those same locations where they are transmitting 460 MHz now.

Just my thoughts.